Sam, the best feather to look at for the basics is Ricochet. It's a very simple shape, all you'll need to cut the HDPE is either a table saw or a jigsaw then drive bolts and shafts through to hold everything together.

Always keep it as simple as possible, the more complex the design, the more likely it is to bugger up and the last thing you want is to have is a twisted chassis/body. As for fixing everything down, make sure you get your measurements and stick to them. Always plan ahead and don't rush it like I did. Best advise I could possibly give.